Treatment of an alkene with mercury acetate in presence of water produce the corresponding alcohol. This reaction is regioselective Markovnikov and stereoespecific anti.

Step 1
. Mercuric acetate dissociation

Step 2. Mercury cation adds to alkene with form a mercurinium ion

Step 3. Water attacks the more substituted carbon to give an alkylmercuric acetate.

Step 4. Replacement of mercury by hidrogen (demercuration)

The product obtained by oxymercuration-demercuration is the same as hydration (H2SO4 /H2O).  However, oxymercuration-demercuration is not susceptible to the rearrangements.